Electrical / electronics question.. any ideas?

[carl0s]

I wonder if anybody has any ideas for this..

 

I have a single pair of wires that I want to use for both power and signalling.

 

I need to do this in an analog / passive way, or at least a very simple and cheap circuit.

 

I want to send ~12v up the wires, but I also want to be able to switch a relay or door-entry solenoid at the other end of the wires, without interrupting the power that's coming up the wires.

 

Any ideas?

[stevie_b]

I don't know much about this, but I'd imagine there would need to be a variance on the "constant" 12v you're loading the wire with.

 

I don't know how they manage to make UK domestic ring-main wiring carry signals: I presume the 50Hz sine wave AC acts as a carrier wave upon which data is superimposed, thus giving a small deviation from a "true" 240v.

 

I guess your application would need something similar. You're helped in that the "data" to be superimposed is much simpler than, say, internet traffic, but may be hindered by the need to hold a constant-ish 12v. I also imagine the voltage is the only thing you can vary in order to transmit the signal to the relay to open/close it.

 

Just my thoughts, they may not be correct.

[carl0s]

I think I might just be forgetting this idea and going another route ..

thanks for the thoughts so far though